1. Field of the Invention
The invention relates to a denture cleansing powder composition and a process for making such a composition.
2. Description of the Related Art
Denture cleansing generally is carried out either by brushing dentures with a paste or by soaking dentures overnight in an aqueous cleansing solution. Aqueous denture cleanser solutions are known and generally comprise tablets, granules, or powders that are dissolved in water to form a cleansing bath or cleansing system in water.
One type of denture cleansing composition uses an effervescent system including sodium bicarbonate, citric acid and/or alkaline proteolytic cleaning enzymes, bleaching or oxidizing agents, such as alkali metal and alkaline earth metal, perborates, e.g. anhydrous sodium perborate and sodium perborate monohydrate (herein "perborates"), and monopersulfates. A second type of denture cleansing composition uses cleaning enzymes and anhydrous sodium perborate in combination with sodium perborate monohydrate. There are no persulfates in this second type of composition.
The cleansing systems produced by both of these compositions when dissolved in water have drawbacks. The pH of the aqueous solution in the first system is too low (i.e. too acidic) for fully effective cleaning enzyme activity. In addition, the reaction of the monopersulfate in the composition with chlorides in the water produces a hypochlorite which inactivates the cleaning enzymes in the composition, further depressing their efficacy. The hypochlorite also reacts with expensive fragrances in the composition, depressing their efficacy.
The use in compositions of perborate monohydrates that do not inactivate proteolytic cleaning enzymes either directly or indirectly is known. However, the use of potassium monopersulfate in the form of "OXONE", in the presence of perborate monohydrate, in a weight ratio of approximately 3:1 has been shown to result in the formation of a sufficient amount of hypochlorite in water to deactivate alkaline proteolytic cleaning enzymes. U.S. Pat. No. 5,118,623 to George Boguslawski and John W. Shultz of Solvay Enzyme Inc., issued Jun. 2, 1992, discloses that many cleaning enzymes are inactivated in the presence of chlorine and other halogens. A paper by Waku et al, CA 78(17):107533p discloses inactivity of enzymes in the presence of as little as 0.2 pans per million free chlorine.
The pH of the aqueous solution in the second system is too high (i.e. too basic). This high pH has a tendency to destroy the fragrance of the cleaning solution. In addition, the pH of the second type of composition may be too high for optimal activity of the cleaning enzyme.
There have been efforts, with limited success, to develop compositions in which deactivation of cleaning enzymes and fragrances do not occur, while good denture cleaning efficacy is still provided.
U.S. Pat. No. 4,409,118 to Anthony Eoga, issued Oct. 11, 1983, discloses an effervescent cleansing composition in tablet form comprising: (1) a phosphate salt; (2) a silicate salt; and (3) at least one perborate salt. At least part of the perborate salt is in a compacted granulated mixture with a polymeric fluorocarbon.
U.S. Pat. No. 4,857,224, to Anthony Eoga, issued Aug. 15, 1989, discloses an effervescent cleansing composition in tablet form comprising: (1) a pregranulated and compressed mixture of an anhydrous perborate, a perborate monohydrate and a polymeric fluorocarbon compound, and (2) a monopersulfate compound. This composition is useful for forming a composition from monopersulfates and anhydrous perborates.